This invention relates generally to a system for monitoring non-coincident, nonstationary process signals. More particularly, this invention relates to a system for monitoring non-coincident, nonstationary process signals used in detecting deficiencies in various stages of manufacturing processes, biological process and the like.
There is often a need or desire to monitor finite length, non-stationary signals that may include repetitive deterministic artifacts that are non-coincident in time. This phenomenon occurs, for example, in many engineering systems that contain moving parts that are monitored by digitizing sensors monitoring signals relevant to the quality of those parts.
For example, an assembly line where the thickness of manufactured plastic or metal components might be measured. In such an example, every component passing through the sensor produces a signal that has a shape that is substantially similar to the preceding signal—but the signal may be longer or shorter depending upon the speed of the conveyor belt. Another example would be the force applied to the die set in a metal stamping machine. Once again, a signal representing this force would possess a similar shape with every repetition of the machine's movement. The length of the force signal, however, may be longer or shorter depending upon how fast the machine is operating. Biological signals may also produce signals with repetitive deterministic artifacts. One such example includes the use of cardiac signals from a biological heart monitored from EKG traces.
In each of the foregoing cases, if one were to digitize and then plot the monitored signals, the length of the repetitive deterministic artifacts would vary from part to part or from cycle to cycle, depending upon the speed and variability of the system or organism being monitored. A reference signal can often be used to compare to these repetitive signal waveforms for detection of anomalies, but only if their lengths are exactly the same. If their lengths are not the same, large discrepancies between the reference signal and the input signal would be seen due to the signals not being coincident. Such discrepancies could result in an erroneous diagnosis.